The use of molecular sieves as catalysts in aromatic conversion processes are well known in the chemical processing and refining industry. Aromatic conversion reactions of considerable commercial importance include the alkylation of aromatic compounds such as in the production of ethyltoluene, xylene, ethylbenzene, cumene or higher alkyl aromatics and in disproportionation reactions such as toluene disproportionation, xylene isomerization, or the transalkylation of polyalkylbenzenes to monoalkylbenzenes.
Various aromatic conversion processes may be carried out either in the liquid phase, the vapor phase or under conditions under which both liquid and vapor phases exist. At the relatively high temperatures involved in vapor phase reactions, it is generally accepted that water present in the feed stream is detrimental to the reaction process, while various reasons are advanced for the adverse impact of water, the most widely observed detrimental effect is probably catalyst deactivation due to dealumination. For example, U.S. Pat. No. 4,197,214 to Chen et al. discloses a process for modifying various crystalline zeolite molecular sieves such as ZSM-5, ZSM-11, ZSM-12, ZSM-35, ZSM-38, faujasite, mordenite, and erionite by the inclusion of metallic ions such as zinc. Chen et al. states that high temperature steam functions by way of a hydrolysis reaction to cause loss of framework aluminum which is accompanied by the loss of the associated protons, leading to a reduction in catalytic activity. The hydrolysis reaction is said to be quite slow at temperatures below about 800.degree. F. However, at higher temperatures above 900.degree. F., the reaction rate is sufficiently fast to affect long-term stability of the zeolite catalyst.
In some cases, water can be tolerated under the high temperature conditions involved in vapor phase reactions. For example, U.S. Pat. No. 4,107,224 to Dwyer discloses the vapor phase ethylation of benzene over zeolite catalysts characterized in terms of those having a constraint index within the approximate range of 1-12. Suitable zeolites disclosed in Dwyer include ZSM-5, ZSM-11, ZSM-12, ZSM-35 and ZSM-38. The Dwyer process involves the interstate injection of ethylene and benzene to offset some of the temperature rise due to the exothermic alkylation reaction. Dwyer states that water and hydrogen sulfide are tolerable if more rapid aging of the catalyst is acceptable, but are moderately detrimental in the process.
Steam stabilized zeolites are disclosed as useful in aromatic conversion processes involving alkylation such as in the production of ethylbenzene or cumene. For example, U.S. Pat. No. 4,185,040 to Ward et al. discloses the alkylation of benzene to produce ethylbenzene or cumene employing zeolites such as molecular sieves of the X, Y, L, B, ZSM-5 and Omega crystal types, with steam stabilized hydrogen Y zeolite being disclosed as the preferred catalyst. In the Ward process, temperature and pressure conditions are employed so that at least some liquid phase is present until substantially all of the alkylating agent is consumed. Ward states that rapid catalyst deactivation occurs under most operating conditions when no liquid phase is present.
The use of steam stabilized zeolites in the production of high molecular weight alkyl benzenes is disclosed in U.S. Pat. No. 4,301,316 to Young. Here relatively high molecular weight alkylating agents having one or more reactive alkyl groups of at least 5 carbon atoms are employed. The reactants may be in either the vapor phase or the liquid phase. The zeolite catalyst may be subjected to modifying treatments involving steaming for periods ranging from about one quarter to about 100 hours in an atmosphere containing from about 5 to about 100% steam.
U.S. Pat. No. 4,774,377 to Barger et al. discloses an aromatic conversion process involving alkylation over a catalyst comprising a solid phosphoric acid component followed by transalkylation aluminosilicate molecular sieve transalkylation catalysts including X-type, Y-type ulstrastable Y, L type, Omega type and mordenite zeolites. Aluminosilicate alkylation catalysts may also be employed. Water in an amount from about 0.01 to 6% by volume of the organic material charged to the alkylation reaction zone may be added. The water is typically removed with the light by-product stream recovered in the first separation zone.
In hydrocarbon conversion processes involving olefin conversion, water may or may not be tolerated in the feed stream depending on the nature of the molecular sieve employed. For example, U.S. Pat. No. 4,551,438 to Miller discloses the oligomerization of olefins over molecular sieves, characterized as intermediate pore size, having an effective pore aperture in the range of about 5 to 6.5 angstroms, such as ZSM-5, ZSM-11 and silicalite, Miller discloses that the feed should be contain less than 100 ppm and preferably less than 10 ppm water as well as being low in sulfur and nitrogen. On the other hand, when employing a somewhat larger pore size molecular sieve, specifically steam stabilized zeolite Y, in the conversion of C.sub.2 -C.sub.12 olefins to motor fuels, water is described as an effective cofeed which stabilizes the catalyst and reduces the deactivation rate. Thus, as described in U.S. Pat. No. 4,740,648 to Rabo et al., co-fed water is described as a particularly desirable diluent which tends to aid in resistance of zeolite Y catalyst to coking and aging.